Solenoid actuated unit injectors for controlling the admission of fuel to diesel engines, particularly heavy duty trucks and marine engines, have been in common use for a number of years. Early on, the fuel control valve for admitting fuel to the pressure chamber of these devices was mechanically actuated. In more recent years, the solenoid actuated control valve has become more popular and useful in light of its quick action and the fact that it can be easily and accurately programmed with current electronically controlled engines and software systems.
In a solenoid actuated unit injector or unit pump or common rail fuel system, there is provided an electromagnetic coil for energizing an armature which is attached to a fuel control valve, which admits fuel to a pressure chamber (either in the pump or in the injector body depending upon the device). Most commonly, the control valve with attached armature plate is spring biased to a normally open position with the electromagnetic coil being in an unenergized state. Upon energization of the electromagnetic coil, a control valve, in the form of a sliding reciprocating valve, is closed momentarily until the electromagnetic coil is next de-energized. Also, the chamber or cavity within which the armature resides is fuel-filled to provide equalization of pressure on all sides of the reciprocating fuel control valve and to allow a certain degree of damping of the action of the armature plate as the electromagnetic coil is repeatedly energized and de-energized. This also helps control valve balance which refers to the action of the control valve returning home on its valve seat as the valve is closed.
In the above-referenced systems, it is common to secure the armature plate to the control valve by means of a flathead counter-sunk screw in such a manner that the screw head faces the surface of the armature that is exposed to the electromagnetic coil and the screw shank is embedded within the control valve.
A further problem experienced with the prior art fuel injection pump assemblies is the difficulty of plugging the ends of fuel flow channels. These fuel flow channels are typically drilled through the body from the sides of the body, and therefore require plugging at the end in which the drill bit entered the body. These flow channels are typically plugged by providing a tapered flow channel, and inserting a tapered plug in the channel. A ring of high temperature solder is placed in the channel adjacent the tapered plug, and the solder melts as the assembly is heat treated. The solder secures the plug in the channel. This process can be unduly costly for the manufacturer.